Alkanes AS

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons with the general formula CₙH₂ₙ₊₂.

Question 2

What is petroleum?

Answer 2

A mixture mainly consisting of alkane hydrocarbons.

Question 3

How is crude oil separated?

Answer 3

Crude oil is vaporized and fed through a column that is hotter at the bottom and cooler at the top, allowing fractions to be collected based on boiling points.

Question 4

What is thermal cracking?

Answer 4

A process that takes place at high temperatures (up to 1000°C) and pressures (up to 70 atm) to produce alkenes from long-chain alkanes.

Question 5

What is catalytic cracking?

Answer 5

A process that occurs at around 500°C and slight pressure in the presence of a zeolite catalyst, mainly producing motor fuels and aromatic hydrocarbons.

Question 6

Why do alkanes have specific boiling points?

Answer 6

Their boiling points depend on chain length and branching; longer chains have more Van der Waals forces, leading to higher boiling points.

Question 7

What is the equation for complete combustion of alkanes?

Answer 7

A: CₙH₂ₙ₊₂ + O₂ → CO₂ + H₂O.

Question 8

What is the equation for incomplete combustion of alkanes?

Answer 8

CₙH₂ₙ₊₂ + O₂ → CO + H₂O.

Question 9

What are the issues with CO₂?

Answer 9

It is a greenhouse gas that contributes to global warming; solutions include burning less fossil fuel.

Question 10

What are the problems associated with CO?

Answer 10

Carbon monoxide is toxic; ensure a good supply of air/oxygen during combustion to minimize this.

Question 11

What are the problems caused by soot?

Answer 11

Soot can blacken buildings and contribute to global dimming; solutions include ensuring adequate air supply during combustion.

Question 12

What problems does sulfur dioxide cause?

Answer 12

It leads to acid rain, damaging trees, buildings, and aquatic life; solutions include removing sulfur from fuels or desulfurizing flue gases.

Question 13

How are nitrogen oxides formed?

Answer 13

Through the reaction of nitrogen and oxygen at high temperatures, often in engines; they also contribute to acid rain.

Question 14

What is flue gas desulfurization?

Answer 14

A process using alkaline slurry (e.g., calcium carbonate) to remove SO₂ from flue gases, forming harmless calcium sulfate.

Question 15

What is a free radical?

Answer 15

A highly reactive particle with an unpaired electron, formed when a covalent bond splits.

Question 16

How is ozone formed in the stratosphere?

Answer 16

UV radiation splits oxygen molecules into free radicals, which react with other oxygen molecules to form O₃.

Question 17

What are CFCs and why are they banned?

Answer 17

CFCs are inert halogenoalkanes that deplete the ozone layer; they were banned due to their harmful environmental effects.

Question 18

What are some alternatives to CFCs?

Answer 18

Hydrofluorocarbons (HFCs) and hydrocarbons are safer substitutes now used in refrigeration and aerosol propellants.

Question 19

What is a halogenoalkane?

Answer 19

A halogenoalkane is an alkane with at least one halogen atom in place of a hydrogen atom.

Question 20

What are some common uses of halogenoalkanes?

Answer 20

Halogenoalkanes are used as solvents, pharmaceuticals, refrigerators, and propellants.

Question 21

What is the general formula for mono-substituted halogenoalkanes?

Answer 21

CnH2n+1X, where X is a halogen.

Question 22

Why is the carbon-halogen bond in a halogenoalkane polar?

Answer 22

Halogens are much more electronegative than carbon, making the carbon atom electron-deficient and prone to attack by nucleophiles.

Question 23

What are nucleophiles?

Answer 23

Nucleophiles are electron-pair donors that attack electron-deficient carbon atoms. Examples include OH-, CN-, and NH3.

Question 24

What occurs during the hydrolysis of halogenoalkanes?

Answer 24

When halogenoalkanes react with an aqueous solution of warm hydroxide ions (OH-) and water, they produce an alcohol and a halide ion.

Question 25

What is the role of hydroxide ions in the hydrolysis of halogenoalkanes?

Answer 25

Hydroxide ions (OH-) donate lone pairs to the electron-deficient carbon, leading to the formation of a covalent bond and the breaking of the carbon-halogen bond.

Question 26

What is formed when halogenoalkanes react with ethanolic potassium cyanide (KCN)?

Answer 26

A nitrile is formed.

Question 27

What is the result of reacting a halogenoalkane with excess ethanolic ammonia?

Answer 27

An amine is formed.

Question 28

What determines the rate of hydrolysis of halogenoalkanes?

Answer 28

The strength of the C-Halogen bond. The C-F bond is the strongest, so fluoroalkanes react slower, while the C-I bond is the weakest, so iodoalkanes react faster.

Question 29

What type of reaction occurs when halogenoalkanes react with hydroxide ions dissolved in ethanol?

Answer 29

An elimination reaction, forming an alkene.

Question 30

What are the main mechanisms for halogenoalkane reactions based on their structure?

Answer 30

• Primary Haloalkanes: Mainly undergo nucleophilic substitution.
• Secondary Haloalkanes: Can undergo both substitution and elimination.
• Tertiary Haloalkanes: Mainly undergo elimination.